This invention was made with government support under Contract No. N00014-96-1-0782 awarded by Ballistic Missile Defense Organization. The Government has certain rights in this invention.
The present invention relates to an improved semiconductor material and a method of its production. More specifically the present invention relates to an amorphous semiconductor alloy including aluminum and gallium and to a method of production that allows for convenient band gap engineering of the alloy and for deposition of the alloy on a variety of vacuum compatible materials.
Crystalline GaN, AlGaAs, GaAs, and InGaP have enjoyed success in a number of electronic and optical applications. For example, light emitting diodes formed of AlGaAs, GaAs, and InGaP have been proposed using epitaxial crystal growth techniques, see U.S. Pat. No. 4,971,928. UV detectors formed of crystalline AlxGa1xe2x88x92xN are proposed in U.S. Pat. No. 4,616,248. The present invention is partially based upon the recognition that the success of these crystalline semiconductor materials is limited by the various processes for their production because these processes necessarily incorporate specific steps to preserve the crystalline state of the semiconductor material.
For example a typical semiconductor deposition scheme is presented in U.S. Pat. No. 3,979,271, where solid layer semiconductor compositions are deposited by simultaneously sputtering and discharge reacting materials and depositing the materials on a heated substrate. The substrate is typically heated above 300xc2x0 C. to provide polycrystalline growth and typically to above 500xc2x0 C. to provide highly oriented, epitaxial growth. Higher temperatures may be needed for epitaxial growth on silicon substrates. The present inventors have recognized that these particular heating steps limit the availability of economical electronic and optical devices including conventional crystalline materials. Accordingly, there is a need for an improved semiconductor material and a more versatile method of depositing such a semiconductor material.
This need is met by the present invention wherein a semiconductor structure and a scheme for engineering a band gap of an amorphous material and forming a layer of the amorphous material on a semiconductor substrate are provided. In accordance with one embodiment of the present invention, a semiconductor structure is provided comprising an amorphous alloy formed over at least a portion of a semiconductor substrate. The amorphous alloy comprises aluminum nitride (AlN) and gallium nitride (GaN) and may be characterized by a band gap between about 3 eV and about 6 eV. The amorphous alloy may be characterized by the following formula:
AlxGa1xe2x88x92xN
where x is a value greater than zero and less than one.
The amorphous alloy may further comprise indium nitride and may be characterized by a band gap between about 2 eV and about 6 eV. A dopant may be incorporated into the amorphous alloy. The dopant may comprise a rare earth element or, more specifically, a rare earth luminescent center.
In accordance with another embodiment of the present invention, a method of forming a layer of amorphous material on a semiconductor substrate is provided. The method comprising the steps of: (i) positioning the semiconductor substrate in a reactive sputter deposition chamber of a reactive sputtering system including at least one sputter target containing aluminum and gallium; (ii) introducing a nitrogen gas into the sputter deposition chamber; (iii) operating the sputtering system to promote reaction of aluminum and gallium from the sputter target and nitrogen from the gas in the sputter deposition chamber; (iv) maintaining the semiconductor substrate at a deposition temperature selected to promote growth of an amorphous aluminum gallium nitride alloy on the semiconductor substrate; and (v) further operating the sputtering system so as to designate relative proportions of aluminum and gallium in the amorphous aluminum gallium nitride alloy.
The sputter target may comprise a single integrated common target, a pair of discrete target portions, where one of the target portions contains aluminum and the other of the target portions contains gallium, or a pair of targets, where one of the targets contains aluminum and the other of the targets contains gallium. The method may further comprise the step of varying the relative proportions of aluminum and gallium in the amorphous aluminum gallium nitride alloy so as to selectively control a band gap of the alloy.
The sputter target may further include indium and the method may further comprise the steps of: (i) operating the sputtering system to promote reaction of aluminum, gallium, and indium from the sputter target and nitrogen from the gas in the sputter deposition chamber; (ii) maintaining the semiconductor substrate at a deposition temperature selected to promote growth of an amorphous indium aluminum gallium nitride alloy on the semiconductor substrate; and (iii) operating the sputtering system so as to designate relative proportions of indium, aluminum, and gallium in the amorphous aluminum gallium nitride alloy.
The method may further comprise the step of introducing a dopant into the amorphous alloy. The dopant may comprise a rare earth element or, more specifically, a rare earth luminescent center.
In accordance with yet another embodiment of the present invention, a semiconductor material is provided comprising an amorphous alloy including amorphous aluminum nitride (AlN) and amorphous gallium nitride (GaN). The amorphous alloy may further include amorphous indium nitride.
Accordingly, it is an object of the present invention to provide an improved semiconductor structure and a convenient scheme for forming a layer of amorphous material on a semiconductor substrate. Other objects of the present invention will be apparent in light of the description of the invention embodied herein.